Digital camera systems that include sensor arrays (pixel sensors) are generally calibrated before being distributed. During calibration, both dead pixels and stuck pixels are identified and electronic circuits within the camera correct this type of pixel corruption.
Other types of defective pixels are difficult to determine including both hot and cold pixels because the amount of corruption is variable, can be small compared to the signal level, and can depend on the underlying signal. Because of the variation in pixel corruption, hot and cold pixels often go unnoticed during calibration and can lead to enhanced errors due to the use of the hot and cold pixels when different scenes are filmed with different parameters (lighting conditions, colors, intensity, distances etc.).
Additionally during usage, digital cameras that include pixel sensor arrays may suffer as the result of sensor age, sensor deterioration, temperature fluctuations and other environmental conditions. These problems are not normally detected during operation and may only be detected in post processing of the digital motion picture sequence.
In traditional filmmaking—where the camera recorded images on celluloid—the gate was the mechanism in the camera that positioned the film behind the lens as it was exposed to light. Occasionally dirt, lint, dust, hair, and other debris would stick in the gate and interfere with the exposure of the film. The potential damage caused by debris in the gate could render a shot unusable.
Traditional filmmakers developed a protocol to address the problem of debris in the gate, called “Check the Gate”. When the director was satisfied with a shot and ready to move to the next shot, the first assistant camera operator would open the camera and examine the gate. If debris or foreign material was found, the camera would be cleaned and the material would be filmed again. If the gate was clean, the director would move on to the next shot.